Adsorptive membranes for nutrient recovery from wastewater: A novel solution for water purification challenges

Abstract

The removal of nutrients, like phosphate and ammonium, from wastewater is crucial for controlling eutrophication and water reuse. Traditional methods have limitations and are often supplemented by additional treatment steps, having a large footprint, consuming energy, and incurring added costs. This study presents a solution with the design of highly permeable (>100 LMH/bar) adsorptive polyacrylonitrile membranes embedded with akageneite (PAN/Ak) and zeolite 13X (PAN/Z) with high affinities for phosphate and ammonium uptake, respectively. The chemical compatibility between polymer and inorganic fillers resulted in highly flexible membranes with dispersed particles. Additionally, the membranes were stable, with no leaching of filler particles and complete recovery of uptake capacities after 5 adsorption/desorption cycles. Batch tests demonstrated that the maximum uptake capacities of PAN/Ak and PAN/Z are 0.4 mmol P/g and 1.2 mmol N/g, respectively, with phosphate uptake attributed to ligand exchange and ammonium to ion exchange. Moreover, the membranes’ ability to capture ions under dynamic flow conditions persists despite the presence of other competing ions, resulting in an initial removal of > 84% for ammonium and 100% for phosphate from a synthetic wastewater with initial concentrations of 2.1 mmol N/L and 0.1 mmol P/L. These membranes offer a unique solution for emerging water purification challenges, as they combine the high permeability of low-pressure membranes with high selectivity towards target ions.